Continuous casting for producing ingots made of titanium or a titanium alloy has conventionally been performed by injecting titanium or a titanium alloy melted by plasma arc melting into a bottomless mold and while solidifying it, withdrawing the resulting ingot downward. As disclosed in Patent Document 1, a molten metal obtained by melting titanium or a titanium alloy is temporarily retained in a retainer called “hearth” and the molten metal is injected into the mold from this hearth.
The hearth is usually a container made of copper and equipped, inside or outside thereof, with a forced cooling mechanism such as water cooing hole in order to prevent titanium from being contaminated. In addition, in order to prevent the molten metal from solidifying in the hearth, the surface of the molten metal in the hearth is heated. The purpose of providing such a hearth is to make the molten metal temperature uniform, prevent the raw material which has remained without being melted from entering the mold, precipitate inclusions and separate them from the molten metal, and reduce variation in the injection amount of the molten metal into the mold due to variation in a melted amount of the raw material.